[Plots.Pie] Add (failing) test for multiple renders erasing labels.
[Plots.Pie] Add (failing) test for multiple renders erasing labels.

softwords/plottable,RobertoMalatesta/plottable,danmane/plottable,iobeam/plottable,iobeam/plottable,gdseller/plottable,palantir/plottable,gdseller/plottable,alyssaq/plottable,RobertoMalatesta/plottable,NextTuesday/plottable,danmane/plottable,jacqt/plottable,palantir/plottable,iobeam/plottable,softwords/plottable,palantir/plottable,alyssaq/plottable,danmane/plottable,onaio/plottable,onaio/plottable,RobertoMalatesta/plottable,onaio/plottable,NextTuesday/plottable,NextTuesday/plottable,jacqt/plottable,softwords/plottable,alyssaq/plottable,gdseller/plottable,jacqt/plottable,palantir/plottable